Zippers are typically mass-produced using two parallel stringers whose facing edges each carry plastic fastener elements that are interlocked together. In order to obtain zippers of the desired length, the fastener stringers are introduced into a device which forms gaps of predetermined length at predetermined locations within the fastener stringers.
Typically such fasteners are mass produced in a manner similar to that disclosed in commonly assigned U.S. Pat. No. 4,932,113. The operation usually begins with a workpiece comprised of two long parallel fastener tapes or stringers whose facing edges each carry a number of plastic fastener elements that are joined i.e., interlocked together. The workpiece is fed into a first machine which removes the joined elements from a predetermined distance at spaced locations on the workpiece to form a series of gaps therein.
Bottom stops are then fitted onto each of the fastener stringers adjacent the first fastener element. Thereafter, a slider is fitted to the fastener elements from the lead edge of each gap so as to separate the fastener elements. Top stops are then applied to an end opposite the bottom stops. Finally, the fastener stringers are generally transversely cut in the approximate center of the gap to separate the fasteners of predetermined length corresponding to the location of the gaps.
Traditionally gaps are formed in the fastener elements by a gapping machine having a transport system in the form of pinch rollers which pulls or advances the workpiece through a guide provided at the upstream end. Downstream thereof is a punch and die system which serves to cut the fastener elements from each of the respective fastener stringers. When the workpiece has been positioned adjacent the punch and die, a clamp located at or adjacent to the area to be gapped is temporarily closed and a cutter works to remove some or all of the fastener elements through a predetermined length. Examples of such an approach to forming gaps in a workpiece may be found in U.S. Pat. Nos.: 5,334,404; 5,177,855; 5,101,551; 4,738,016; 4,663,817; 4,627,318; 4,625,375; 4,604,783; 4,242,785; and 4,206,669.
Subsequently, a new approach for forming gaps in a workpiece was developed by Applicant in commonly assigned U.S. Pat. Nos. 4,091,532 and 4,019,240 which are hereby incorporated by reference. These patents disclose the use of a gapping machine which provides a clamp which clamps the opposite sides of the portion of the stringer to be gapped, and a hinged block which pivots relative to the clamped fastener stringers to pull off or remove seriatim a plurality of the fastening elements in the area to be gapped. Variations of this approach may be found in U.S. Pat. Nos. 4,325,185 and 4,236,293, Japanese Patent Nos. 60-142,806 and 60-142,807, and U.K. Patent Application No. 2,041,072.
Regardless of which approach is used to form the gaps, it is important to obtain gaps of uniform length. Several methods have developed to obtain gaps of uniform length. One approach has been to use a counter to determine the location of the preceding gap. For example, U.S. Pat. Nos. 4,019,240 and 4,091,532 commonly assigned to Applicant, disclose a gapper device having a fastener chain gap sensing device positioned downstream from the gapper at a predetermined distance corresponding to the desired distance between gaps. The device includes a pivotally mounted lever which is spring biased so as to urge a tip of the lever into engagement with the fastener elements being pulled through the gapper machine and a micro switch operably connected thereto. When the lever senses a gap, the lever pivots to operate the switch to initiate another gapping cycle.
An alternative approach has been to rely on some form of a detection roller or measuring wheel which cooperate with a sensor or counter to determine the distance between gaps. Examples of such an approach is disclosed in U.S. Pat. No. 5,335,404 to Osaki et al., U.S. Pat. No. 5,177,855 to Shimai, U.S. Pat. No. 5,101,551 to Rademacher et al., U.S. Pat. No. 4,625,375 to Osaki, and U.S. Pat. No. 4,604,783 to Kojima et al. Unfortunately, by relying on any of the above disclosed approaches to determine the distance between gaps still requires the use of additional equipment to actually advance the fastener stringers to the predetermined location.
Another area of concern in forming gaps is to prevent damage to the fastener elements immediately adjacent the upstream and downstream ends of the gap. If either the upstream or downstream fastener elements are damaged during gapping, then an extra step is required during the manufacturing process to remove these partial fastener elements prior to applying the top and bottom stops.
One approach to ensuring that the fastener elements immediately adjacent the gap to be formed will not be damaged is disclosed in U.S. Pat. No. 5,335,404 to Osaki et al. which uses a pair of positioning pins located on the upstream and downstream side of the cutting unit. Each positioning pin has an approach sensor for detecting whether or not the distal end of the positioning pin has been inserted between adjacent fastener elements. A selectively rotatable drive motor is moved either forward or backward to ensure that the positioning pins are correctly inserted between fastener elements.
U.S. Pat. No. 4,627,318 to Hochlehnert et al. discloses another approach to solving this problem. The Hochlehnert et al. gapper device has a pair of spring mounted grippers, each having a pin extending therefrom to be positioned between adjacent fastener elements. If a pin lands directly atop a fastener element, the springs of the grippers will cause the grippers outward movement until the pin is properly positioned. The consequence of using any of the above-described approaches to avoid damaging the upstream and downstream fastener elements requires the addition of expensive and complicated locating and/or positioning equipment which not only increases the cost of product but also may result in additional production time to reposition the workpiece.
In conjunction with the need to ensure gaps of uniform length and the need to avoid damaging the upstream and downstream fastener elements of each gap, it is important to be able to readily adjust the gapper device to accommodate gaps of varying lengths and accommodate fastener stringers of different gauges. This is especially true in today's demanding manufacturing climate where production runs of a particular type and gauge of zipper changes frequently, often several times during a single production day. The ability to quickly adjust the gapper device to a different gap length and/or a different gauge i.e., size of zipper is important to minimizing waste material and downtime.